diff -u b/core/lib/Drupal/Core/Menu/LocalActionManager.php b/core/lib/Drupal/Core/Menu/LocalActionManager.php
--- b/core/lib/Drupal/Core/Menu/LocalActionManager.php
+++ b/core/lib/Drupal/Core/Menu/LocalActionManager.php
@@ -130,7 +130,7 @@
    * @param \Drupal\Core\Session\AccountInterface $account
    *   The current user.
    * @param \Drupal\Core\Render\RendererInterface $renderer
-   *   The renderer service.
+   *   The renderer.
    */
   public function __construct(ControllerResolverInterface $controller_resolver, RequestStack $request_stack, RouteMatchInterface $route_match, RouteProviderInterface $route_provider, ModuleHandlerInterface $module_handler, CacheBackendInterface $cache_backend, LanguageManagerInterface $language_manager, AccessManagerInterface $access_manager, AccountInterface $account, RendererInterface $renderer) {
     // Skip calling the parent constructor, since that assumes annotation-based
diff -u b/core/lib/Drupal/Core/Menu/LocalTaskManager.php b/core/lib/Drupal/Core/Menu/LocalTaskManager.php
--- b/core/lib/Drupal/Core/Menu/LocalTaskManager.php
+++ b/core/lib/Drupal/Core/Menu/LocalTaskManager.php
@@ -132,7 +132,7 @@
    * @param \Drupal\Core\Session\AccountInterface $account
    *   The current user.
    * @param \Drupal\Core\Render\RendererInterface $renderer
-   *   The renderer service.
+   *   The renderer.
    */
   public function __construct(ControllerResolverInterface $controller_resolver, RequestStack $request_stack, RouteMatchInterface $route_match, RouteProviderInterface $route_provider, ModuleHandlerInterface $module_handler, CacheBackendInterface $cache, LanguageManagerInterface $language_manager, AccessManagerInterface $access_manager, AccountInterface $account, RendererInterface $renderer) {
     $this->factory = new ContainerFactory($this, '\Drupal\Core\Menu\LocalTaskInterface');
diff -u b/core/modules/system/config/schema/system.schema.yml b/core/modules/system/config/schema/system.schema.yml
--- b/core/modules/system/config/schema/system.schema.yml
+++ b/core/modules/system/config/schema/system.schema.yml
@@ -359,10 +359,10 @@
   mapping:
     primary:
       type: boolean
-      label: 'Whether primary tabs is shown'
+      label: 'Whether primary tabs are shown'
     secondary:
       type: boolean
-      label: 'Whether secondary tabs is shown'
+      label: 'Whether secondary tabs are shown'
 
 condition.plugin.request_path:
   type: condition.plugin
diff -u b/core/modules/system/src/Plugin/Block/SystemLocalActionsBlock.php b/core/modules/system/src/Plugin/Block/SystemLocalActionsBlock.php
--- b/core/modules/system/src/Plugin/Block/SystemLocalActionsBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemLocalActionsBlock.php
@@ -15,7 +15,7 @@
 use Drupal\Core\Routing\RouteMatchInterface;
 
 /**
- * Provides a block to display the page actions.
+ * Provides a block to display the local actions.
  *
  * @Block(
  *   id = "system_local_actions_block",
@@ -101,10 +101,11 @@
   public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
     $form = parent::buildConfigurationForm($form, $form_state);
 
-    // The "Page actions" block is never cacheable because of hooks creating
-    // local actions doesn't provide cacheability metadata.
+    // The "Local actions" block is never cacheable because hooks creating local
+    // actions don't provide cacheability metadata.
+    // @todo Remove after local action hooks provide cacheability metadata.
     $form['cache']['#disabled'] = TRUE;
-    $form['cache']['#description'] = $this->t('This block is never cacheable because of missing cacheability metadata.');
+    $form['cache']['#description'] = $this->t('This block is never cacheable.');
     $form['cache']['max_age']['#value'] = 0;
 
     return $form;
diff -u b/core/modules/system/src/Plugin/Block/SystemTabsBlock.php b/core/modules/system/src/Plugin/Block/SystemTabsBlock.php
--- b/core/modules/system/src/Plugin/Block/SystemTabsBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemTabsBlock.php
@@ -13,7 +13,7 @@
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
- * Provides a block to display the page tabs.
+ * Provides a "Tabs" block to display the local tasks.
  *
  * @Block(
  *   id = "system_tabs_block",
@@ -83,8 +83,9 @@
 
     // The "Page actions" block is never cacheable because of hooks creating
     // local tasks doesn't provide cacheability metadata.
+    // @todo Remove after local task hooks provide cacheability metadata.
     $form['cache']['#disabled'] = TRUE;
-    $form['cache']['#description'] = $this->t('This block is never cacheable because of missing cacheability metadata.');
+    $form['cache']['#description'] = $this->t('This block is never cacheable.');
     $form['cache']['max_age']['#value'] = 0;
 
     return $form;
diff -u b/core/modules/system/src/Tests/Menu/LocalTasksTest.php b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
--- b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
+++ b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
@@ -25,11 +25,11 @@
   public static $modules = ['block', 'menu_test', 'entity_test'];
 
   /**
-   * The local tasks block used for testing.
+   * The local tasks block under testing.
    *
    * @var \Drupal\block\Entity\Block
    */
-  protected $block;
+  protected $sut;
 
   /**
    * {@inheritdoc}
@@ -37,7 +37,7 @@
   protected function setUp() {
     parent::setUp();
 
-    $this->block = $this->drupalPlaceBlock('system_tabs_block', ['id' => 'tabs_block']);
+    $this->sut = $this->drupalPlaceBlock('system_tabs_block', ['id' => 'tabs_block']);
   }
 
   /**
@@ -69,7 +69,7 @@
   }
 
   /**
-   * Asserts that te local tasks on the specified level is not being printed.
+   * Asserts that the local tasks on the specified level are not being printed.
    *
    * @param int $level
    *   (optional) The local tasks level to assert; 0 for primary, 1 for
@@ -175,9 +175,9 @@
    */
   public function testLocalTaskBlock() {
     // Remove the default block and create a new one.
-    $this->block->delete();
+    $this->sut->delete();
 
-    $this->block = $this->drupalPlaceBlock('system_tabs_block', [
+    $this->sut = $this->drupalPlaceBlock('system_tabs_block', [
       'id' => 'tabs_block',
       'primary' => TRUE,
       'secondary' => FALSE,
@@ -195,8 +195,8 @@
     // Verify that local tasks in the second doesn't appear.
     $this->assertNoLocalTasks(1);
 
-    $this->block->delete();
-    $this->block = $this->drupalPlaceBlock('system_tabs_block', [
+    $this->sut->delete();
+    $this->sut = $this->drupalPlaceBlock('system_tabs_block', [
       'id' => 'tabs_block',
       'primary' => FALSE,
       'secondary' => TRUE,
reverted:
--- b/core/modules/system/templates/block--system-page-actions-block.html.twig
+++ /dev/null
@@ -1,18 +0,0 @@
-{% extends "@block/block.html.twig" %}
-{#
-/**
- * @file
- * Default theme implementation for page local actions.
- *
- * Available variables:
- * - action_links: Actions local to the page, such as "Add menu" on the menu
- *   administration interface.
- *
- * @ingroup themeable
- */
-#}
-{% block content %}
-  {% if action_links %}
-    <nav class="action-links">{{ action_links }}</nav>
-  {% endif %}
-{% endblock %}
reverted:
--- b/core/modules/system/templates/block--system-page-tabs-block.html.twig
+++ /dev/null
@@ -1,16 +0,0 @@
-{% extends "@block/block.html.twig" %}
-{#
-/**
- * @file
- * Default theme implementation for page tabs.
- *
- * Available variables:
- * - tabs: The Tabs linking to any sub-pages beneath the current page (e.g., the
- *   view and edit tabs when displaying a node).
- *
- * @ingroup themeable
- */
-#}
-{% block content %}
-  {{ tabs }}
-{% endblock %}
diff -u b/core/themes/seven/templates/page.html.twig b/core/themes/seven/templates/page.html.twig
--- b/core/themes/seven/templates/page.html.twig
+++ b/core/themes/seven/templates/page.html.twig
@@ -62,21 +62,12 @@
         <h1 class="page-title">{{ title }}</h1>
       {% endif %}
       {{ title_suffix }}
-      {% if page.primary_tabs %}
-        <nav class="tabs" role="navigation" aria-label="{{ 'Tabs'|t }}">
-          {{ page.primary_tabs }}
-        </nav>
-      {% endif %}
+      {{ page.primary_tabs }}
     </div>
   </header>
 
   <div class="layout-container">
-    {% if page.secondary_tabs %}
-      <nav class="tabs" role="navigation" aria-label="{{ 'Tabs'|t }}">
-        {{ page.secondary_tabs }}
-      </nav>
-    {% endif %}
-
+    {{ page.secondary_tabs }}
     {{ page.breadcrumb }}
     <main class="page-content clearfix" role="main">
       <div class="visually-hidden"><a id="main-content" tabindex="-1"></a></div>
only in patch2:
unchanged:
--- /dev/null
+++ b/core/themes/classy/templates/block/block--system-page-actions-block.html.twig
@@ -0,0 +1,18 @@
+{% extends "@block/block.html.twig" %}
+{#
+/**
+ * @file
+ * Default theme implementation for page local actions.
+ *
+ * Available variables:
+ * - action_links: Actions local to the page, such as "Add menu" on the menu
+ *   administration interface.
+ *
+ * @ingroup themeable
+ */
+#}
+{% block content %}
+  {% if action_links %}
+    <nav class="action-links">{{ action_links }}</nav>
+  {% endif %}
+{% endblock %}
only in patch2:
unchanged:
--- /dev/null
+++ b/core/themes/classy/templates/block/block--system-page-tabs-block.html.twig
@@ -0,0 +1,16 @@
+{% extends "@block/block.html.twig" %}
+{#
+/**
+ * @file
+ * Default theme implementation for page tabs.
+ *
+ * Available variables:
+ * - tabs: The Tabs linking to any sub-pages beneath the current page (e.g., the
+ *   view and edit tabs when displaying a node).
+ *
+ * @ingroup themeable
+ */
+#}
+{% block content %}
+  {{ tabs }}
+{% endblock %}